Brake vacuum help

[Phils69 27]

I visited my engine guy and went for a test drive after the cam, head and carb swap. All I can say is WOW. It pulls like a big block and I will investing in some tires shortly. As I had feared the cam does not generate the necessary vacuum for the power barkes to work well. They seem to work OK when first applied but fade as the engine gets to idle. I am thinking of trying a vacumm canister first and if that does not work go with a pump setup. Does anybody have a suggestion on a canister? The setup is below:

 

Stroked 408W approx 10.5:1 comp

Holley 750 DP

Weiand Stealth ported intake

AFR 205 heads

2500 Stall convertor

Custom roller cam:

Intake Exhaust

Valve Adjustment: .000†.000â€

 

Lobe Lift: .373†.367â€

Gross Valve Lift 1.60 Ratio: .598†.587â€

 

Duration @ .050†Tappet Lift: 230* 242*

 

Lobe Separation: 111*

 

 

Recommended Intake Centerline: 108*

 

Specs at 108 Degree Intake Centerline:

Valve Timing at Open Close

.050†Tappet Lift: Intake: 7* BTDC 43* ABDC

Exhaust: 55* BBDC 7* ATDC

[LindenBruce 27]

Good to hear you need tires already. I guess you have a good combination. Congrats!! Try the vacuum canister but it prolly won't work in the end but it's cheap and easy to try. Let us know. Bruce

[rangerdoc 22]

Stupid question, but if your car originally had power brakes isn't there already a canister under the passenger wheel well?

 

Edit: I just realized I have that because of my a/c...at least I think that is why I have it. But either way, that is a stock option for you to do.

Edited August 12, 2012 by rangerdoc

[69gmachine 15]

The specs on your cam are very similar to mine although your cam is a tad more aggressive. I'm running 232i and 240e @ .050 on a 112 LSA with .565i and .574e. I haven't had any issues with my booster, and I'm running a single plane.

 

Have you checked to make sure the booster doesn't have a slow leak? Perhaps at idle it isn't pulling enough to overcame the rate of a slow leak. It would be a shame for your cam to be just a hair over the line on what the booster needs.

[Phils69 27]

The car was a stock 4 drum and just put the power kit on it at the same time all this engine work was being done. The engine guy is going to adjust the valves again and wrap up a few things so I don't have the car home yet. I believe the vacuum is being pulled from the big port off the back of the carb right now. Maybe I'll switch it straight to the manifold to see if I gain anything? Like 69g says I'm hoping I'm right on the line and the canister will work well. I've done some research and it seems the pumps can make a lot of noise. Probaly will have to mount it near the exhaust to cover it if I go that route. 69g, what fuel pump are you using? My engine guy is a little worried with my mechanical being able to keep up at sustained high rpms.

[69gmachine 15]

I'm using a carter mechanical pump with 1/2" line from the tank to the pump and 3/8" line from the pump to the carb. I radiused the outlet on the pump to help with flow. I can't remember if I modified the pump for AN fittings or just screwed in adapters. Otherwise the pump is stock.

[Phils69 27]

Well I have a Carter also but used the existing stock hard lines under the car. May need to upgrade to the larger lines. Don't want it starving for fuel but I want to stay away from the electric.

[1969 Mach1 14]

The OEM canister rengerdoc is refering to only came on cars with factory A/C. It may have also came on cars with some type of vacuum assisted tilt steering column. I don't have personal experience with the addition of an aftermarket canister but everybody I have spoke to that tried them said they don't completely cure the problem. With those duration numbers, a cam with a 112 LSA like gmachine has would be a better choice if vacuum is a concern. One degree more on LSA will reduce the overlap two degrees and can mean the difference in motor characteristics between tollerable to drive and a good driver.

Edited August 13, 2012 by 1969 Mach1

[Phils69 27]

I'll get a can and try it. Guess it can't hurt to try for the $. Thanks guys

[LoneWolf2U 136]

Phil, The can is for the interior controls only and will do nothing for the brake system power.

Provided the booster and check valve are working properly, You may have to raise the idle speed slightly.

 

I'm running a Comp 282S, While I just love the galloping idle it has in neutral at 800 rpms. It drops the vacume down to low to keep the booster charged for a second or third pedal pump on the brakes.

 

So I had to run rpm to 950 at idle to keep the vac level up some.

Sometimes a little tweaking can save you a bundle of money.

[Phils69 27]

When I get the car back I'll try raising the idle and see what it will do. I have been doing some research and it appears the initial timing can have an effect also. I remember him saying he set the timing at 10 degrees now. Some have had success raising it 2 to 4 degrees. Maybe raising the timing, without pinging, and the idle will make a difference. I'll probaly have to raise the idle some anyhow for drivability as that cam does have a hard hit to it. Just need the car back to start playing with it.